Ngons and Triangles

What is an Ngon?

An ngon is a face or polygon that is made up of five or more sides or edges connected by five or more vertices. Anything over a quad (4 sides) is considered an ngon.

What is a Triangle? 

A face that consists of just 3 sides or edges connected by 3 vertices. 

Right in the middle of these two types polygons is the quad, which is a face or polygon made up of four sides or edges connected by four vertices. This is the kind you should strive to create.

However, as you're adding edge loops, resolution and shaping your geometry into what you want to make it's almost impossible not to run into triangles and ngons, just make sure to fix them once you are done.